Pls Help. My husband and I want a back-up pump system that is no maintenance and highly reliable. (I don't know anything about our existing pump, except that it is 4rs old. What kinda pump specs should I look for?

Related questions: What's important - gallons per minute, horsepower of the pump, auot recharge, hrs of pumping time, type of battery, etc.? Will a narrow sump limit my choices? And how do I pick an installer?